Hello, when gcc emits vague linkage data for C++ like vtables it makes them all weak. Is there some reason why this needs to be done?
If I'm getting it right, based on e.g. on the comment in binutils/bfd/elf.c saying that they are weak in order to allow multiple copies and that the GNU ld extension linkonce will discard all but one, this seems to be done only for historical reasons (or call that compatibility, whatever). With the usual setup of using the complete GNU toolchain, there will be always only one such symbol because of the linkonce feature in each resulting binary/library. If there will be more such libraries each of them having the same symbol, the normal ELF symbol rules will bind all references only to one of them, and those symbols are all the same anyway. Which means that in such case there's no reason to have those symbols weak, and having them weak means that the symbol lookup in ld.so for them will be more expensive (because it has to search all libraries for a non-weak symbol only to find out there's obviously no such thing). Is there some reason why this shouldn't be changed to have these symbols emitted normally as non-weak? On a somewhat related note, I've been looking at how to better control emitting of such vague linkage data. It's not that difficult to have many of these things emitted in many places, which I expect should lead to things like longer build times, larger binaries, even more conflicts with prelink, non-unique symbols problems if one doesn't (want to) use RTLD_GLOBAL and such (well, I don't just expect the last two ones to happen - they do). Info pages info:/gcc/Vague Linkage and info:/gcc/C++ Interface are quite helpful on this, so I think I'll try the effect of #pragma interface/implementation . However the docs give me kind of the impression that this is not really the recommended way of doing things - is there some better way or are there any problems with these pragmas I should expect? I also wonder about the exact effect of these on templates, those pages and info:/gcc/Template Instantiation are a bit unclear (and obsolete?) on this topic. From my test it seems those pragmas don't have any special effect as far as templates are concerned - am I right on this? Thanks gcc --version : gcc (GCC) 4.0.2 20050901 (prerelease) (SUSE Linux) -- Lubos Lunak KDE developer --------------------------------------------------------------------- SuSE CR, s.r.o. e-mail: [EMAIL PROTECTED] , [EMAIL PROTECTED] Drahobejlova 27 tel: +420 2 9654 2373 190 00 Praha 9 fax: +420 2 9654 2374 Czech Republic http://www.suse.cz/
